Anode compositions

ABSTRACT

In accordance with certain of its aspects, this invention relates to novel processes and to a lead base alloy suitable for anode production consisting essentially of lead and tin and at least one metal selected from the group consisting of tellurium, thallium, and cadmium and containing 90-99 percent by weight of lead, 1-7 percent by weight of tin, and at least one metal selected from the group consisting of tellurium, thallium, and cadmium in an amount of 0.005-5.0 percent by weight sufficient to bring the total weight of the lead base alloy anode to 100 percent.

United States Patent [191 Seyb et al. I

[ ANODE COMPOSITIONS [22] Filed: Nov. 5, 1971 [2]]. Appl. No.: 196,206

Related US. Application Data [62] Division of Ser. No. 830,851, June 5,1969,

[73] Assignee: M & T Chemicals Inc., New York,

abandoned.

[52] US. Cl 204/51, 204/293 [51] Int. Cl C231) 5/06, BOlk 3/06 [58]Field of Search t. 204/51, 293

[56] References Cited UNITED STATES PATENTS 1,766,87l 6/l930 Beckinsaleet al. 75/166 C 2,060,534 ll/l936 Singleton et al. 75/166 R 2,841,5417/1958 Smith 204/51 2,729,602 l/l956 Van Houton 204/55 R Aug. 28, 1973FOREIGN PATENTS OR APPLICATIONS 508,604 7 7/1939 Great Britain 75/166 BOTHER PUBLICATIONS Transactions of the Electrochemical Soc., Vol. 80,pp. 59 and 60 by Bray et al., 1941.

Primary Examiner-F. C. Edmundson Attorney-Lewis C. Brown, Kenneth GWheeless et al. I

57 f ABSTRACT In accordance with certain of its aspects, this inventionrelates to novel processes and to a lead base alloy suitable for anodeproduction consisting essentially of lead and tin and at least one metalselected from the group 9 Claims, No Drawings 1 ANODE COMPOSITIONS Thisapplication is a divisional application of Ser. No. 830,85l, filed June5, 1969,'now abandoned.

This invention relates to novel anodes, novel anode compositions, and tothe preparation of such anodes and their use in electroplatingprocesses. More particularly, this invention relates to the preparationand use of novel lead base alloy anodes containing 90-99 percent byweight of lead, 1-7 percent by weight of tin,

and at least one metal selected from the group consist-- in order toprovide anodes which carry a higher surface current density thanconventional anodes of equal cross-sectional area and to reduce thebuild-up upon the anode of undesirable deposits such as chromatedeposits. During the course of chromium plating operations, lead anodesbecome heavily coated with lead ox: ides (mainly lead dioxide, PbO Whenleft standing in a solution containing chromic acid, a lead anodeordinarily becomes coated with lead chromate and such coatings act topartially insulate the anode, thusinterfering with the normaldistribution of the chromium deposited on the cathode. Such defects areespecially undesirable in industrial chromium plating whereirregularities in current distribution may produce wide variations inchromium plate thicknesses. During conventional operations, therefore,it may become necessary to remove such incrustations from conventionallead anodes by wire brushing or by chemical treatment using solutionscontaining hydrochloric acid or aqueous solutions containingalkali-metal pyrophosphate or other cleaning agents.

it is an object of the present invention to provide an improved leadalloy anode which is essentially free of antimony, bismuth, and arsenic.Another object of the invention is to provide an improved chromiumelectroplating process using a lead base alloy anode whichisparticularly resistant toattack by chromic acid. A further object of theinvention is to provide a lead base alloy anode which gives superiorchromium electrodeposits and is characterized by particularly long lifewhen subjected to the corrosive attack of chromic acid and otherchromium plating bath chemicals.

In accordance with certain of its aspects, this invention relates tonovel processes and to a lead base alloy suitable for anode productionconsisting essentially of lead and tin and at least one metal selectedfrom the group consisting of tellurium, thallium, and cadmium andcontaining 90-99 percent by weight of lead, 1-7 percent by weight oftin, and at least one metal selected from the group consisting oftellurium, thallium, and cadmium in an amount of 0005-50 percent byweight sufficient to bring the total weight of the lead base alloy anodeto 100 percent.

The lead base alloy anodes of the invention are particularlycharacterized by the substantial absence of antimony, bismuth, andarsenic from the alloy. The lead base alloy anodes of the invention arepreferably at least ternary alloys consisting essentially of lead, tin,and tellurium or thallium, or cadmium, or combinations of one or more ofthese last three metals. Typical lead base alloy anodes may about 90-98percent by weight of lead, about 2-5 percent by weight of tin, and theremainder tellurium (typically in amounts sufficient to saturate thealloy) or thallium (typically in amounts up to 1 percent by weight), orcadmium (typically in amounts up to 2 percent by weight). Higherpercentages of tin, tellurium, thallium, or cadmium may be usedaccording to the invention, but cost considerations generally do notjustify the use of excessive amounts of these metals.

The lead base alloy anode compositions are prepared by melting themetals together or by adding and dissolving the metals for a particularalloy in molten lead and then cooling the resulting lead base alloyanode composition. 1

The leadbase alloy anodes prepared according to the invention have goodhardness properties, excellent electricalproperties (including goodinitial resistance during startup'periods in chromium plating process)and are particularly resistant to attack by chromic acid during thechromium electroplating process. The lead base alloy anodes'areexceptionally resistant to attack 'in' chromic acid which containsadditives such as sulfates, fluorides, and especially mixed radicalssuch as sulfate SO, and silicofluoride SiFf.

Typical lead alloy anode compositions which may be employed according tothe invention and which have been found superior to prior art lead baseanodes include the following examples which are summarized in 30 TableI. In Table I all parts are given in percent by weight based upon thetotal weight of the lead base alloy.

TABLE I Typical chromium plating baths in which the lead base alloyanode compositions of the invention may be employed may contain fromabout -600 g/l of chromic acid (as Crll Illustrative acidic aqueouschromium plating baths which may be employed include the following bathcompositions:

Preferred Component Amount Concentrations l Chromic acid 750-600 50Sulfate ion (e.g. from sulfuric acid) 1-10 2.5 [I Chromic acid l50-6002S0 Sulfate ion (e.g. from sulfuric acid) 0.5-5 1 Silicofluoride ion(e.g. from H,SiF.) l-l0 2 [ll Chromic acid 150-600 400 Sulfate ion (e.g.from strontium sulfate) 1-5' 2 Silieofluoride ion (e.g. from H,SiF.) 2-85 Another aspect of the invention relates to a process forelectrodepositing chromium from an aqueous acidic chromiumelectroplating bath which contains at least one chromium compoundproviding chromium metal ions for electroplating chromium whichcomprises passing current from a lead base alloy anode consistingessentially of lead, tin, and at least one metal selected from the groupconsisting of tellurium, thallium,

was greater than 0.50 grams per square centimeter were classified aspoor. As can readily be seen from Table II, lead base alloy anodecompositions prepared in accordance with the invention herein showedgood resistance to attack in chromic acid solutions. In addition, thelead base alloy anode compositions of the invention possess excellentinitial-resistance characteristics and provide excellent chromium platedarticles.

TAB LE 11 Lead Base Alloy Anode Compositions l 2 3 4 5 6 7 8 9 Ex. No.Control Meta] (Percent by Weight) Pb 97.95 96.0 97.0 96.995 94.0 96.22594.525 94.50 100.0 Sn 2.0 2.0 2.0 2.0 3.0 3.0 4.0 4.0 Te 0.05 0 0 0.0050 0.025 0.025 0.05 0 Tl 0 0 1.0 0.5 1.0 0.75 0 0.50 0 Cd 0 2.0 0 0.5 2.00 1.450 0.95 0

TOTAL 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Anode Weight Loss GJcm. 0.27 0.22 0.27 0.25 0.20 0.22 0.19 0.20 0.79

and cadmium, wherein said lead base alloy anode contains 90-99 percentby weight lead, l-7 percent by weight tin, and the remainder of saidlead base alloy anode consists of at least one metal selected from thegroup consisting of tellurium, thallium, and cadmium to a cathodethrough said aqueous acidic chromium plating solution to produce achromium surface on at least a portion of said cathode.

Chromium electroplating is ordinarily carried out with the novel leadbase alloy anode of the invention using bath temperatures of l-95 C. andplating currents of l-60 amperes per square decimeter (asd).

The following examples are submitted for the purpose of illustrationonly and are not to be construed as limiting the scope of the inventionin any way.

GENERAL PROCEDURE Lead base alloy anodes were prepared by melting theindicated amounts of lead and tin together and then adding the indicatedamount of tellurium, thallium, and

cadmium to obtain a metal solution. The so-formed alloy was then' castinto cold molds or extruded to the desired shape of the anode.

All of the lead base alloy anode compositions described in theillustrative examples possess superior hardness and resistivity againstattack from chromic acid solutions when compared with the controlanodes.

Resistance to chromic acid attack was measured by immersing an anodeinto a solution of chromic acid containing 240 g/l of chromic acid andthe mixed radicals, sulfate, and silicofluoride at a temperature of 43C. for a time of 120 hours. During this time the solutions wereelectrolyzed with an anode current density of amperes per squaredecimeter (asd) foreight.

Another control consisting of a binary alloy containing 90 percent Pband 10 percent Sb exhibited a corresponding loss of 0.70 g/cm.

As can be seen from Table II, lead-base alloy anodes of the inventionpossess good resistance to attack in chromic acid solutions.

We claim: 1. A process for electrodepositing chromium from an aqueousacidic chromium electroplating bath which contains at least one chromiumcompound providing hour periods and then let stand for 16 hours. At theend of 120 hours, the anodes were removed and the weight loss of eachdetermined. The loss of anode weight was measured after removal ofdeposits formed on said anode by side reactions such as the reaction ofthe chromium metal ions for electroplating chromium which comprisespassing current from a lead base alloy anode consisting essentially oflead, tin, and at least one member selected from the group consisting oftellurium, thallium, and cadmium, wherein said lead base alloy anodecontains 90-99 percent by weight lead, l-7 percent by weight tin, andthe remainder of said lead base alloy anode consists of at least onemember selected from the group consisting of tellurium, thallium, andcadmium to a cathode through said aqueous acidic chromium-platingsolution to produce a chromium surface on at least a portion of saidcathode.

2. A process as claimed in claim 1 wherein the chromium electroplatingbath contains sulfate SO, and silicofluoride SiF,.

3. A process as claimed in claim 1 wherein the lead base alloy anodecontains 0.000-005 percent tellunum.

4. A process as claimed in claim 1 wherein the lead' base alloy anodecontains 0.000-l.0 percent thallium. 5. 'A process as claimed in claim 1wherein the lead base alloy anode contains 0.0002.0 percent cadmium.

anode with the chromic acid. Anodes wherein the loss of anode materialwas less than 0.35 grams per square centimeter of immersed anode surfacewere considered good and anodes wherein the loss of anode material 6. Aprocess as claimed in claim 1 wherein the lead base alloy anode contains0.000-005 percent tellurium. and 0.000-l.0 percent thallium.

7. A process as claimed in claim 1 wherein the lead base alloy anodecontains 0.000-0.05 percent tellurium and 0000-20 percent cadmium.

A process as claimed in claim 1 wherein the lead base alloy anodecontains 0.0000.05 percent tellubase alloy anode contains 0.000-l.0percent thallium rium, 0.000l.0 percent thallium, and 0.0002.0 perand0.0002.0 percent cadmium. cent cadmium.

9. A process as claimed in claim 1 wherein the lead

2. A process as claimed in claim 1 wherein the chromium electroplatingbath contains sulfate SO4 and silicofluoride SiF6 .
 3. A process asclaimed in claim 1 wherein the lead base alloy anode contains 0.000-0.05percent tellurium.
 4. A process as claimed in claim 1 wherein the leadbase alloy anode contains 0.000-1.0 percent thallium.
 5. A process asclaimed in claim 1 wherein the lead base alloy anode contains 0.000-2.0percent cadmium.
 6. A process as claimed in claim 1 wherein the leadbase alloy anode contains 0.000-0.05 percent tellurium and 0.000-1.0percent thallium.
 7. A process as claimed in claim 1 wherein the leadbase alloy anode contains 0.000-0.05 percent tellurium and 0.000-2.0percent cadmium.
 8. A process as claimed in claim 1 wherein the leadbase alloy anode contains 0.000-1.0 percent thallium and 0.000-2.0percent cadmium.
 9. A process as claimed in claim 1 wherein the leadbase alloy anode contains 0.000-0.05 percent tellurium, 0.000-1.0percent thallium, and 0.000-2.0 percent cadmium.